What is Peripheral Neuropathy?

The term peripheral neuropathy is used to describe a variety of conditions affecting the nerves in the peripheral nervous system. The peripheral nervous system is in the arms and legs. The symptoms of peripheral neuropathy include pain, numbness, tingling, burning and weakness. It can be caused by a number of conditions including trauma, metabolic disorders, alcoholism, cancer chemotherapy and infection. Sometime, peripheral neuropathy is called idiopathic because the cause is not known.

peripheral neuropathyThe peripheral nervous system serves an important function, which is to make the person aware that there is possible tissue damage or a dangerous element in their immediate environment. Normal function of the nervous system is such that pain is an indicator of imminent or actual harm to a body part, which results in protective reflexes that will either prevent or minimize the damage. The term for this type of pain is nociceptive pain. It’s generally described as sharp, aching, throbbing type of pain. When pain occurs without any noxious stimuli or threat of imminent harm, this is termed neuropathic pain. It is maladaptive or dysfunctional and does not serve any purpose for the nervous system. Typically, the sensations are described as tingling, shooting, or stinging.

The nervous system is comprised of two parts; the central nervous system, which includes the brain, spinal cord and peripheral nervous system (which includes all the nerves apart from the brain and spinal cord). Peripheral neuropathy affects the peripheral nerves. The peripheral nervous system has two parts; the somatic nervous system and the autonomic nervous system. The somatic nervous system exerts control over the skeletal muscles and allows us to exert voluntary control over our bodies. The autonomic nervous system controls automatic and involuntary functions of the body, which include control of our cardiovascular systems, respiratory systems, digestion and urinary tract systems. These systems all work to maintain homeostasis, which is the state of equilibrium. We do not have control over this and therefore it is outside of our conscious control, hence the term autonomic. In the peripheral nervous system there are two major types of nerves. There are the motor nerves and the sensory nerves. The motor nerves carry electrical impulses from the brain to the peripheral skeletal muscles. The sensory nerves carry messages from the periphery; the arms, the legs, the organs, to the spinal cord and brain.

Structure of Peripheral Nervous System

The peripheral nerve cells have three parts. Each nerve cell, or neuron, has a cell body, which is also called a soma, dendrites, which are fibers which extend from the cell body and are the sensory input for the neuron, as well as the axon, otherwise known as a nerve fiber. This projects from the cell and transfers the signal from the cell body to an adjacent nerve or muscle cell. These axons are in two types. They can either be myelinated or unmyelinated. Myelin is a fatty sheath that insulates the axon and improves conductivity. There are two types of nerve fibers. They may either be large or small. The large nerve fibers are typically myelinated and long. Myelination, or insulation of the nerve fibers, allows them to carry nerve signals at a very rapid rate to the central nervous system. There are typically not associated with pain. Large nerve fibers are responsible for motor function, vibration perception, positional sense and perception of temperature. When the large fibers don’t work well dysfunction is characterized by numbness, tingling, weakness and loss of deep tendon reflexes.

Small nerve fibers can be either myelinated or unmyelinated. These small nerve fibers are typically very sensitive to pain and abnormal sensations. These abnormal sensations may be tingling or burning. Small fiber neuropathy symptoms may include pain, altered sensation, pressure or insensitivity to heat/cold. The pain may be described as burning or stabbing. The altered sensations may be described as warmth, coldness, honey or a warm fluid dripping down the leg or bugs crawling on the leg. Autonomic dysfunction may also occur with small nerve dysfunction. Autonomic dysfunction is change in controls of our normal homeostasis of the cardiovascular, respiratory, digestive or urinary tract systems. Most commonly, small fiber neuropathy is idiopathic, that is its cause is unknown.

What happens in peripheral neuropathy?

In peripheral neuropathy there is a dysfunction or abnormal function of the nerves in the peripheral nervous system. The symptoms associated with peripheral neuropathy depend on which nerves are affected. Remember that there are three types of nerves in the peripheral nervous system. There are the sensory nerves, the motor nerves and the peripheral nerves. The sensory nerves relate to providing sensory input from the periphery of the body to the central nervous system. If the sensory nerves are damaged this may lead to pain, numbness, tingling, burning or a loss of sensation. Typically, the symptoms start in the legs or the hands and move centrally towards the trunk. The nerve damage can either be in the large or the small fibers. The symptoms may be either continuous or intermittent. If there is lack of sensation this can lead to multiple recurrent injuries that may not be immediately noticed because the limbs are numb.

"The pain may be described as burning or stabbing. "

This can lead to permanent damage including damage to the skin, chronic infections, poor healing and loss of limbs. If the motor nerves are damaged, then there may be loss of control over the arms or legs. This can be noted as weakness, discoordination or heaviness. This may progressively worsen over time depending on the damage. If the autonomic nervous system peripheral nerves are damaged, then there may be symptoms related to the cardiac, respiratory, gastrointestinal or urinary tract. These symptoms may include heart rate irregularities, blood pressure changes, inability to regulate body temperature, sweating abnormalities, dizziness, bowel dysfunction resulting in either constipation or diarrhea, sexual dysfunction or blurred vision.

 

Peripheral Neuropathy Classification

There are three classifications of neural neuropathy which include mononeuropathy, multiplex mononeuropathy and polyneuropathy. Simply, mononeuropathy means one nerve or the involvement of a single (peripheral) nerve. Carpal tunnel syndrome is the most common cause of mononeuropathy and it may be a result of nerve entrapment or trauma. Mononeuropathy multiplex is a term used when there are more than one peripheral nerves in separate areas of the body that are affected by peripheral neuropathy. There are a number of medical conditions that are associated with mononeuropathy multiplex including vasculitis, diabetic amyotrophy, sarcoidosis, Lyme’s disease, lymphoma carcinoma, HIV, amyloidosis and polyarteritis nordosa.

Polyneuropathy

Polyneuropathy affects multiple nerves and usually in more than one extremity and more than one side of the body. The symptoms are typically in the legs and the arms. Polyneuropathy is associated with the following conditions: diabetes, alcoholism, vitamin D deficiency and HIV. There’s a type of polyneuropathy that is termed distal symmetric polyneuropathy. There are two types of polyneuropathy. It may either be acute or chronic. Acute polyneuropathy comes on suddenly and becomes rapidly progressive. Typical conditions associated with acute polyneuropathy include: Guillain–Barré Syndrome, diphtheria, vasculitis, tumor, porphyria and medication therapy. Polyneuropathy evolves over a much longer time period. This is associated with diabetes, which is the most common cause, nutritional deficiencies, cancer, renal failure, medication toxicity and alcohol abuse.

Risk factors for Neuropathy

Risk factors for development of polyneuropathy include diabetes. Sixty percent of patients with diabetes, type I or II, develop peripheral neuropathy. There seems to be a correlation between the control of elevated blood sugars. Poor control of blood sugar leads to a marked increase in the risk of onsite of peripheral neuropathy autoimmune diseases include: Systemic lupus erythematosus (SLE), rheumatoid arthritis and Guillain–Barré Syndrome. There are also risk factors with metabolic diseases such as amyloidosis and hypothyroidism, hereditary disorders, Charcot-Marie-Tooth’s disease. Infectious disease such as HIV, hepatitis B, leprosy, Lyme’s disease, ischemic disorders, chronic kidney or liver failure, trauma or compression of a nerve, repetitive motion disorder, vitamin deficiencies including B12, alcohol abuse, paraneoplastic disorders, toxic substance exposure, chemotherapy including vinca alkaloids, platinum-based drugs and taxanes; all of the above are risk factors and are associated with the increased incidence of peripheral neuropathy development. Incidents of peripheral neuropathy estimates as high as 20 million Americans suffer from some type of peripheral neuropathy. This is a approximately 8% of our adults over the age of 55. Worldwide, the incidents of peripheral neuropathy are estimated to range from 2-10% of the population. Approximately 25-60% of diabetics are thought to have some type of diabetic peripheral neuropathy with estimates varying widely. Worldwide, the most common cause of neuropathy is leprosy with HIV infection gaining rapidly.

Diabetic Neuropathy

In the western countries the most common cause of peripheral neuropathy is diabetes mellitus; both type I and type II. The peripheral neuropathy occurs in approximately 30-50% of diabetic patients as estimated by the American Academy of Family Physicians. The characteristic symptoms of diabetic peripheral neuropathy include loss of sensation, typically in a stocking glove pattern. This typically starts in the feet and spreads towards the trunk. Symptoms include burning, tingling and aching that worsens at night. Other symptoms may include allodynia, which is pain from light touch that is typically not painful in normal patients, and hyperalgesia, which is termed as an increased sensitivity to painful stimuli. Diabetic neuropathy is related to hypoglycemia and insulin deficiencies, but the mechanism of nerve damage is not known

"The peripheral neuropathy occurs in approximately 30-50% of diabetic patients as estimated by the American Academy of Family Physicians."

Risk factors for diabetic peripheral neuropathy include a long duration of the disease, poor control of blood sugars and obesity. Other risk factors include hypertension, smoking, dyslipidemia with elevations of cholesterol and triglycerides. The common characteristics of diabetic neuropathy include numbness, reduced sensation, pain, burning, pins and needles, shooting pain, hyperesthesia, pain worsening at night, poor posture control, hyperextension of the big toe and clawing of the toes, reduced thickness of the plantar tissue and foot ulcers.

Foot Ulcerations and Diabetes

Foot ulcerations are a serious complication of diabetic peripheral neuropathy. The causes are reduced sensation in the feet, reducing the reflexes and mechanisms or reduction in circulation, changes in gait and abnormalities of movements causing abnormal pressure points. Diabetic neuropathy also affects nearly 50% of diabetics. The autonomic neuropathy is typically associated with cardiac disease. Diabetic focal neuropathy may include the following symptoms: inability to focus the eye, double vision, aching behind one eye, Bell’s Palsy, severe pain in the low back or pelvis, pain in the front of the thigh, pain on the outside of the shin or the foot and chest or abdominal pain. Remission or resolution of pain from diabetic peripheral neuropathy is related to change of the metabolic status that is better control of blood sugars, weight loss and sensory loss that is not severe.

Pre-diabetes and Peripheral neuropathy

There has been a renewed focus on elevated blood sugars and pre-diabetes as it relates to the development of peripheral neuropathy. Mounting research evidence shows that elevated blood sugars may be related to damage of peripheral nerves. The neuropathy associated with pre-diabetes or poor glucose control is the same type that diabetics suffer from. The following symptoms occur in both pre-diabetics and diabetics, which include tingling, paraesthesia, pain, numbness and autonomic dysfunction. The symptoms with pre-diabetes are typically lessened as compared to those with diabetes. Metabolic syndrome is common in pre-diabetes. Metabolic syndrome is characterized by excess weight around the waist, high triglycerides, dyslipidemia, high blood pressure and high fasting blood glucose levels.

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